Method and apparatus for instrument propulsion

ABSTRACT

Embodiments generally relate to propulsion tube units and propulsion devices for progressing instruments along passages, and associated methods of use. For example, the instruments may include, tools, sensors, probes and/or monitoring equipment for medical use (such as endoscopy) or industrial use (such as mining). In some embodiments, the propulsion device may comprise an elongate tube defining a channel configured to accommodate a liquid and a pressure actuator in communication with the channel. The pressure actuator may be configured to selectively adjust a pressure of the liquid in the channel to alternatingly: reduce the pressure to induce cavitation and form gas bubbles in the liquid; and increase the pressure to collapse some or all of the gas bubbles back into the liquid, thereby accelerating at least part of the liquid towards the first end of the tube and transferring momentum to the tube to progress the tube along the passage.

TECHNICAL FIELD

Embodiments generally relate to propulsion tube units and propulsiondevices for progressing instruments along passages, and associatedmethods of use. For example, the instruments may include, tools,sensors, probes and/or monitoring equipment for medical use (such asendoscopy) or industrial use (such as mining). The described embodimentsmay also be suitable for applications in other fields to progress aninstrument along a passage.

BACKGROUND

There are a number of existing methods and apparatus for progressinginstruments along passages including applications in mining and inmedicine, such as endoscopy. There are a number of difficulties withprogressing conventional endoscopic equipment along a tract or lumen ina patient, and these difficulties may carry associated risks of causingdamage to the patient.

It is desired to address or ameliorate one or more shortcomings ordisadvantages associated with existing propulsion devices forprogressing instruments along passages, or to at least provide a usefulalternative.

Any discussion of documents, acts, materials, devices, articles or thelike which has been included in the present specification is not to betaken as an admission that any or all of these matters form part of theprior art base or were common general knowledge in the field relevant tothe present disclosure as it existed before the priority date of eachclaim of this application.

Throughout this specification the word “comprise”, or variations such as“comprises” or “comprising”, will be understood to imply the inclusionof a stated element, integer or step, or group of elements, integers orsteps, but not the exclusion of any other element, integer or step, orgroup of elements, integers or steps.

SUMMARY

Some embodiments relate to a propulsion device for progressing aninstrument along a passage, the propulsion device comprising:

an elongate tube comprising a first end and a second end opposite thefirst end, the tube defining a channel configured to accommodate aliquid, a first end of the channel being closed at or near the first endof the tube and a second end of the channel being defined by the secondend of the tube; and

a pressure actuator in communication with the second end of the channeland configured to selectively adjust a pressure of the liquid in thechannel to alternatingly:

-   -   reduce the pressure to induce cavitation and form gas bubbles in        the liquid; and    -   increase the pressure to collapse some or all of the gas bubbles        back into the liquid, thereby accelerating at least part of the        liquid towards the first end of the tube and transferring        momentum to the tube to progress the tube along the passage.

Some embodiments relate to a propulsion tube unit comprising:

an elongate tube comprising a first end and a second end opposite thefirst end, the tube defining a channel configured to accommodate aliquid, a first end of the channel being closed at or near the first endof the tube and a second end of the channel being defined by the secondend of the tube; and

a piston assembly connected to the second end of the tube, the pistonassembly comprising:

-   -   a body defining a bore in fluid communication with the channel        of the tube; and    -   a movable piston disposed within the bore and configured to seal        against an internal surface of the bore,

wherein the piston assembly and the tube cooperate to define a sealedvessel containing a selected mass of liquid and a selected mass of gas.

The piston assembly may be configured for cooperation with an actuatorto effect movement of the piston to selectively adjust a pressure of theliquid in the channel to alternatingly: reduce the pressure to inducecavitation and form gas bubbles in the liquid; and increase the pressureto collapse some or all of the gas bubbles back into the liquid, therebyaccelerating at least part of the liquid towards the first end of thetube and transferring momentum to the tube to progress the tube alongthe passage.

In some embodiments, the propulsion device or propulsion tube unit maycomprise one or more mechanisms configured to promote cavitation in oneor more regions of the channel when the pressure is reduced, wherein theone or more regions extend along at least part of a length of thechannel. The one or more mechanisms may be configured to promotecavitation in a plurality of regions spaced along at least part of thelength of the channel. The one or more mechanisms may comprise a surfacevariation on an internal surface of the channel.

The surface variation may comprises a coating. The coating may comprisea hydrophobic material. The coating may comprise a catalytic material.The coating may comprise one or more coatings selected from:octadecyltrichlorosilane, silane compounds, Parylene C, flouropolymers,PTFE (Teflon™), manganese oxide polystyrene (MnO2/PS), nano-compositezinc oxide polystyrene (ZnO/PS), nano-composite precipitated calciumcarbonate, fluorinated acrylate oligomers, urethane, acrylic,polyvinylpyrrolidone (PVP), polyethylene oxide, combinations ofhydroxyethylmethacrylate, and acrylamides, or other hydrophobiccompounds.

The surface variation may comprise a topographical variation. Thetopographical variation may have a surface roughness in the range ofabout 0.1 μm to 500 μm, about 0.5 μm to 100 μm, or about 1 μm to 10 μm,for example.

The topographical variation may comprises a scratched or pitted surface.The topographical variation may define a plurality of V-shaped channels.A characteristic angle of the V-shaped channels may be in the range ofabout 10° to 90°, about 30° to 60°, or about 40° to 50°, for example. Anaverage width of the V-shaped channels may be in the range of about 1 μmto 10 μm, or about 2 μm to 4 μm, for example.

The topographical variation may define a plurality of conical pits. Acharacteristic angle of the conical pits may be in the range of about10° to 90°, about 30° to 60°, or about 40° to 50°, for example. Anaverage width of the conical pits may be in the range of about 1 μm to10 μm, or about 2 μm to 4 μm, for example.

The topographical variation may define a plurality of protrusions. Anaverage height of the protrusions may be in the range of about 0.1 μm to1 mm, about 1 μm to 500 μm, or about 10 μm to 100 μm, for example. Anaverage width of the protrusions may be in the range of about 0.1 μm to500 μm, about 0.5 μm to 100 μm, or about 1 μm to 10 μm, for example. Anaverage distance between adjacent protrusions may be in the range ofabout 0.1 μm to 500 μm, about 0.5 μm to 100 μm, or about 1 μm to 10 μm,for example.

In some embodiments, the protrusions may comprise nanowires or hollownanotubes which may be formed of materials such as carbon or silicon,for example.

For nanowire, the width of the protrusions may be in the range of about10 nm to 500 nm, about 20 nm to 300 nm, or about 100 nm to 200 nm; thelength or height of the protrusions 835 may be in the range of about 0.1μm to 100 μm, about 1 μm to 50 μm, or about 10 μm to 20 μm; and theaverage spacing between protrusions may be in the range of about 10 nmto 10 μm, about 10 nm to 100 nm, or about 100 nm to 1 μm, for example.

For nanotubes, the width of the protrusions may be in the range of about10 nm to 100 nm, about 10 nm to 50 nm, or about 20 nm to 40 nm; thelength or height of the protrusions may be in the range of about 1 μm to50 μm, about 5 μm to 30 μm, or about 10 μm to 20 μm; the pore size (orinternal diameter) of the protrusions may be in the range of about 1 μmto 40 μm, about 5 μm to 30 μm, or about 10 μm to 20 μm; and the averagespacing between protrusions may be in the range of about 10 nm to 10 μm,about 10 nm to 100 nm, or about 100 nm to 1 μm, for example.

The topographical variation may define a porous surface. The poroussurface may comprise a foam, sintered material or other porous material,for example. An average pore size of the porous surface may be in therange of about 10 nm to 200 μm, about 20 nm to 250 nm, about 50 nm to150 nm, about 10 μm to about 200 μm, or about 50 μm to about 100 μm, forexample. The porous surface may comprise a layer of porous material. Thethickness of the porous layer may be in the range of about 10 μm to 1mm, or about 50 μm to 100 μm, for example.

The one or more mechanisms may comprise a variation in a thermalconductivity of a wall of the tube along the length of the channel. Thethermal conductivity of the wall may vary along the length of thechannel over a range of about 0.25 Wm⁻¹ K⁻¹ to 240 Wm-1 K-1.

The one or more mechanisms may comprise one or more acoustictransducers. The one or more of the acoustic transducers may be disposedwithin a wall of the tube. The one or more of the acoustic transducersmay be disposed outside of a wall of the tube. An operating frequency ofthe acoustic transducers may be in the range of about 1 kHz to 100 kHz.A power associated with insonation energy directed to a lumen of thechannel by the acoustic transducers may be in the range of about 10 mWto 100 mW.

In some embodiments, the propulsion device may be configured forprogressing a medical instrument along a lumen within a patient.

In some embodiments, the channel may be a continuous enclosed channelextending from the first end of the tube to the second end of the tube.The tube may be reinforced against expansion or contraction due tointernal pressure changes. The tube may be formed of a material suitablefor sterilisation.

In some embodiments, the propulsion device may comprise a plurality oftubes according to any one of the described embodiments extending sideby side.

In some embodiments, the pressure actuator may comprise a flexiblemembrane defining a sealed chamber and a driving mechanism configured todeform the flexible membrane to selectively adjust the pressure of theliquid in the channel.

In some embodiments, the pressure actuator may comprise a pistonassembly including a moveable piston disposed within a bore of thepiston assembly; and a driving mechanism configured to drive the pistonof the piston assembly to selectively adjust the pressure of the liquidin the channel. The piston assembly may be connected to the tube to forma sealed tube unit containing the liquid, and the piston assembly may beremovably coupleable to the driving mechanism.

Some embodiments relate to a propulsion tube unit comprising one or moreof the tubes according to any one of the described embodiments; and

a piston assembly connected to the second end of the tube, the pistonassembly comprising:

-   -   a body defining a bore in fluid communication with the channel        of each of the one or more tubes; and    -   a movable piston disposed within the bore and configured to seal        against an internal surface of the bore.

Some embodiments relate to a propulsion tube unit comprising: one of thetubes according to any one of the described embodiments; and

a movable piston disposed within the channel at or near the second endof the tube and configured to seal against an internal surface of thechannel.

In some embodiments, the piston assembly and the one or more tubes maycooperate to define a sealed vessel containing a selected mass of liquidand a selected mass of gas. The selected masses of liquid and gas may bechosen for a particular length and diameter of the tube. The liquid andgas may be held at a predetermined pressure not significantly higherthan a typical channel pressure during operation.

Some embodiments relate to a drive console comprising:

a housing defining a socket configured to receive and engage apropulsion tube unit according to any one of the described embodiments;

an actuator configured to engage the piston; and

a controller configured to operate the actuator to move the piston toselectively adjust a pressure within the channel of the tube.

Some embodiments relate to a method of progressing an instrument along apassage, the method comprising selectively adjusting a pressure of aliquid within a tube connected to the instrument to successively inducecavitation of gas bubbles in the liquid and subsequently collapse thegas bubbles back into the liquid to accelerate the liquid within thetube, transfer momentum from the liquid to the tube, and progress thetube along the passageway.

BRIEF DESCRIPTION OF DRAWINGS

Exemplary embodiments will now be described in detail with respect tothe drawings, in which:

FIG. 1 is a schematic diagram of a propulsion device according to someembodiments;

FIGS. 2A to 2F are a series of longitudinal sections of a portion oftube of a propulsion device showing a cycle of nucleation and cavitationof gas bubbles within a liquid contained within the tube, and subsequentcollapse of the gas bubbles back into the liquid, according to someembodiments;

FIGS. 3A to 3G are a series of longitudinal sections of a portion oftube of a propulsion device showing a cycle of nucleation and cavitationof gas bubbles within a liquid contained within the tube, and subsequentcollapse of the gas bubbles back into the liquid, according to someembodiments;

FIG. 4 is a longitudinal section of a portion of tube of a propulsiondevice illustrating mechanisms for promoting bubble nucleation and/orcoalescence in certain regions within the tube, according to someembodiments;

FIG. 5 is a longitudinal section of a portion of tube of a propulsiondevice illustrating mechanisms for promoting bubble nucleation and/orcoalescence in certain regions within the tube, according to someembodiments;

FIG. 6 is a longitudinal section of a portion of tube of a propulsiondevice illustrating mechanisms for promoting bubble nucleation and/orcoalescence in certain regions within the tube, according to someembodiments;

FIG. 7 is an illustration of a topographical surface variation forpromoting bubble nucleation, according to some embodiments;

FIGS. 8A to 8E show a series of illustrations of different types ofprotrusions for promoting bubble nucleation, according to someembodiments;

FIG. 9 is an illustration of a porous surface for promoting bubblenucleation, according to some embodiments;

FIGS. 10A to 10C show a series of illustrations of different types oflarge scale topographical surface variations for enhancing momentumtransfer between the liquid and the tube, according to some embodiments;

FIG. 11 shows exemplary displacement and velocity profiles illustratingthe movement of a piston of a pressure actuator, according to someembodiments;

FIG. 12 shows an exemplary pressure cycle illustrating the pressureapplied to the liquid in the tube, according to some embodiments;

FIGS. 13A and 13B show cross-sections of two devices with a plurality oftubes illustrating different arrangements of the tubes, according tosome embodiments;

FIG. 14 shows a schematic diagram of part of a propulsion device with aremovable tube and piston assembly, according to some embodiments;

FIG. 15 shows a front panel of a drive console of the propulsion deviceof FIG. 14;

FIG. 16 shows an endoscopic system including the propulsion device ofFIG. 14, according to some embodiments; and

FIG. 17 shows a propulsion device with an alternative tube unitaccording to some embodiments.

DESCRIPTION OF EMBODIMENTS

Embodiments generally relate to propulsion devices for progressinginstruments along passages, and associated methods of use. For example,the instruments may include, tools, sensors, probes and/or monitoringequipment for medical use (such as endoscopy) or industrial use (such asmining). The described embodiments may also be suitable for applicationsin other fields to progress an instrument along a passage.

Referring to FIG. 1, a propulsion device 100 is shown according to someembodiments. The propulsion device 100 comprises an elongate tube 110defining a lumen or channel 120 configured to accommodate a liquid 130,and a pressure actuator 140 configured to selectively adjust a pressureof the liquid 130 in the channel 120, such as by varying the pressure,optionally varying the pressure continuously.

A first or distal end 122 of the channel 120 is closed at or near afirst or distal end 112 of the tube 110. The distal end 112 of the tube110 is shown disposed in a channel or lumen 101 of a passage 103 in FIG.1.

In some embodiments, the tube 110 may be configured to be inserted intoand through a biological tract, such as a lumen 101 of a passage 103 ofa patient. Examples of such biological tracts include the oesophagus,stomach, bowel, colon, small intestine, large intestine, duodenum, orany one or more passages of the gastro-intestinal system. In someembodiments, the tube 110 may be configured for insertion into andthrough another passage 103 in a patient, such as blood vessels, veinsor arteries, for example. In some embodiments, the tube 110 may beconfigured for human medical applications or veterinary applications. Insome embodiments, the tube 110 may be configured for industrialapplications, such as for use in plumbing pipes, wall cavities, cabletracks, machinery, mining or wellbores, for example.

In some embodiments, the tube 110 may be configured to be accommodatedwithin an insertion tube of an endoscope, and the insertion tubeconfigured to be inserted into a passage 103, such as a passage in apatient. An example of such an arrangement is illustrated in FIG. 16.The tube 110 of the propulsion device 100 may be accommodated within apropulsion tube channel (not shown) within the insertion tube. In someembodiments, the propulsion tube channel may be concentric or coaxialwith the outer diameter of the insertion tube, and may extend along acentral longitudinal axis of the insertion tube. In some embodiments,the propulsion tube channel may be radially offset from the central axisof the insertion tube.

The pressure actuator 140 is in communication with a second or proximalend 124 of the channel 120 at or near a second or proximal end 114 ofthe tube 110 opposite the distal end 112. The channel 120 may comprise acontinuous enclosed channel extending from the first end 112 of the tube110 to the second end 114 of the tube 110.

The pressure actuator 140 may comprise any suitable device configured toselectively adjust a pressure of the liquid 130 in the channel 120, suchas a reciprocating piston, for example. In some embodiments, thepressure actuator 140 may comprise a piston driven by a motor, such as alinear motor, controlled by a controller (not shown).

The pressure actuator 140 may be configured to gradually reduce thepressure within the channel 120 to induce cavitation and form gasbubbles in the liquid 130, and then to suddenly increase the pressure tocompress and collapse the gas bubbles back into the liquid 130, therebyaccelerating at least part of the liquid 130 towards the first end 112of the tube 110, such that momentum is transferred from the liquid tothe tube 110 to progress the tube 110 along a passage.

In some embodiments, when the channel 120 is at an initial or basepressure, there may be volumes of gas and liquid 130 within the channel120, and the pressure actuator 140 may be controlled to increase thepressure to compress and dissolve part or all of the gas into the liquid130. In some embodiments, the channel 120 may be entirely filled withthe liquid 130, and the pressure actuator 140 may reduce the pressure toinduce cavitation of gas out of the liquid 130. In various embodiments,the base pressure may be set: at or near atmospheric pressure;significantly higher than atmospheric pressure; or significantly lowerthan atmospheric pressure.

The pressure actuator 140 may be configured to adjust the pressure in arepeating cycle to induce cavitation of gas bubbles out of the liquid130 and subsequently compress part or all of the gas back into theliquid 130. In various applications, the difference between the maximumpressure in the channel 120 and the minimum pressure in the channel 120may be in the range of about 10 kPa to 100 MPa, about 10 kPa to 100 kPa,about 100 kPa to 1 MPa, about 1 MPa to about 10 MPa, or about 10 MPa toabout 100 MPa, for example. In some embodiments, the maximum pressuremay be above, below or close to atmospheric pressure. In someembodiments, the minimum pressure may be above, below or close toatmospheric pressure but having a non-zero difference from the maximumpressure.

For example, for gastro-intestinal applications, the channel pressuremay vary from 100 kPa below atmospheric pressure to 1000 kPa aboveatmospheric pressure; for cardiovascular applications, the channelpressure may vary from 20 kPa below atmospheric pressure to 300 kPaabove atmospheric pressure; for industrial applications, the channelpressure may vary from 1000 kPa below atmospheric pressure to 10000 kPaabove atmospheric pressure.

The liquid 130 in the channel 120 may comprise any one or more of: apure liquid, a solution, a gas/liquid solution (i.e., a gas dissolved inliquid), a mixture of gas and liquid, a mixture of liquid and solidparticles, such as a suspension, and a mixture of two or more miscibleor immiscible liquids, for example. In some embodiments, the volumetricratio of gas to liquid at atmospheric pressure may be in the range ofabout 0.1% to 10%, about 0.5% to 5%, or about 1% to 2%, for example.

The liquid 130 may comprise any suitable liquids, gases, solid particlesor solutions, such as: water, ethanol, carbon dioxide, nitrogen, air,nitric oxide, argon, salts, sodium chloride, potassium formate, acids,acetic acid, or lithium metatungstate, for example.

Different liquids may be suitable for different applications. Forexample, in medical applications, preferred liquids may bebiocompatible, non-toxic (or have very low toxicity), non-pyrogenic,non-inflammatory, not highly osmotic, relatively inert, and be suitablefor operation at relatively low pressures and at temperatures similar tothe typical temperature of a patient. For example, water, ethanol,carbon dioxide, nitrogen, air, nitric oxide, argon.

In industrial applications where biocompatibility is not required,liquids with higher densities may be preferred, such as aqueoussolutions of inert inorganic compounds, for example. One suitable highdensity liquid may be an aqueous solution of lithium metatungstate whichhas high density, low viscosity, and good thermal stability.

In various embodiments, the tube 110 may be formed of differentmaterials depending on their suitability for a given application. Forexample, for medical applications, the tube 110 may be formed of anon-toxic material which is sufficiently flexible to bend around cornersor turns in a passage within the body of a patient.

Some examples of materials which may be used to form the tube 110 indifferent applications include: polymers, plastics, polyethylene, highdensity polyethylene, polytetrafluoroethylene, vinyl, nylon, rubber,elastomers, resins or composite materials comprising textilesimpregnated with polymers, elastomers or resins. Polymers containingvoids (foams) in the internal structure may also be used to increaseflexibility such as extruded polytetrafluoroethylene (ePTFE). Compositelayering of these materials may also be used to increase strengthmaintain flexibility and resist internal pressure or kinking.

A wall 118 of the tube 110 should have a strength and thicknesssufficient to withstand the expected range of pressure differentials fora given application. In some embodiments, the tube 110 or tube wall 118may be reinforced to mitigate against expansion and/or contraction ofthe tube due to pressure changes. Any suitable reinforcing material maybe used, such as high strength fibres or ultra-high molecular weightpolyethylene, for example.

Referring to FIGS. 2A to 2F, a segment of the tube 110 of the propulsiondevice 100 is shown according to some embodiments, illustrating thecavitation process in a series of diagrams.

Referring to FIG. 2A, at an initial or base pressure, the channel 120may be substantially or entirely filled with the liquid 130 with littleor no gas within the channel 120. (Although, in some embodiments, theremay be a significant volume of gas present in the channel at the basepressure).

When the pressure in the channel 120 is gradually reduced by thepressure actuator 140, gas bubbles 133 may begin to form in the liquid130 within the channel 120, as shown in FIG. 2B. The gas bubbles 133 maycomprise gas that was previously dissolved in the liquid 130 and/orvapour (i.e., a gas phase of the liquid 130). The bubbles 133 may formthrough homogeneous nucleation or through heterogeneous nucleation inthe liquid 130 on nucleation sites, such as particles suspended in theliquid 130 and/or at nucleation sites on an inner surface 126 of thetube 110.

As the pressure is reduced further, the bubbles 133 may grow in volumeto form larger bubbles 133 c, as shown in FIG. 2C, and new bubbles 133may continue to be formed through nucleation. Some of the bubbles 133,133 c may coalesce to form even larger bubbles 133 d, as shown in FIG.2D.

Under certain conditions, the bubbles 133 may coalesce to form a largebubble 133 e which spans a lumen of the channel 120, as shown in FIG.2E. That is, the spanning bubble 133 e may take up the entire lumen ofthe channel 120 in a region of the channel 120 such that differentportions of the liquid 130 are separated on either side of the bubble133 e. It may be desirable to encourage or promote the formation of suchspanning bubbles 133 e in the channel 120, as this may enhance orincrease the propulsive effect by increasing the acceleration of theliquid 130 during the sudden increase of pressure, and thus increasingthe kinetic energy imparted to the liquid 130 and the momentumtransferred to the tube 110.

When the pressure is increased (i.e., during compression) the liquid 130is accelerated in a distal direction (i.e., towards the first or distalend 122 of the channel 120), as indicated by arrows 201 in FIG. 2F. Dueto the relatively high compressibility of the gas bubbles 133, which isorders of magnitude higher than the relatively low compressibility ofthe liquid 130, the liquid 130 is allowed to accelerate quickly andcompress the bubbles 133, as shown in FIG. 2F.

When the bubbles 133 are compressed, they experience a sudden increasein pressure and density, and collapse (i.e., dissolve and/or condense)back into the liquid 130, as shown in FIG. 2A. The rate ofdissolution/collapse of the bubbles 133 into the liquid 130 may beincreased by increasing the total surface area of the gas-liquidinterfaces. Therefore, it may be desirable to encourage or promote theformation of many bubbles 133, and preferably many spanning bubbles 133e.

There are a number of ways in which the likelihood of the formation ofspanning bubbles 133 e may be increased, several of which are discussedbelow. For example, in some embodiments, one or more additives may beincluded in the liquid 130 to enhance bubble coalescence. In someembodiments, the internal diameter of the channel 120 may be selected tobe relatively small so that only relatively small bubble volumes arerequired to span the lumen. However, the internal diameter of the lumenshould still be large enough to allow the liquid 130 to flow along thechannel 120 when the pressure is suddenly increased (i.e., not be toolimited by capillary resistance). In some embodiments, the propulsiondevice 100 may comprise a plurality of tubes 110 extending side by sidewith each other, and each defining a channel 120. This may allow theinternal diameter of each channel 120 to be relatively small whilemaintaining a relatively high total mass of liquid 130 within the tubes110.

In some embodiments, cavitation, bubble nucleation and/or bubblecoalescence may be enhanced, encouraged or promoted in certain regionsof the channel 120.

In some embodiments, the propulsion device 100 may comprise one or moremechanisms configured to promote cavitation, bubble nucleation and/orbubble coalescence in one or more regions of the channel when thepressure is reduced. The one or more regions may extend along at leastpart of a length of the channel 120. For example, the one or moremechanisms may be configured to promote cavitation, bubble nucleationand/or bubble coalescence in a plurality of regions spaced along thelength of the channel 120.

In some embodiments, each region where cavitation is promoted may extendalong part of the channel length by a distance of between about 10% and400% of an internal diameter of the channel 120, optionally about 30%and 300%, optionally about 50% and 200%. In some embodiments, a distancebetween adjacent regions where cavitation is promoted may be greaterthan the internal diameter of the channel 120 by a factor of about 2 to50, about 5 to 30, or about 10 to 20, for example.

Referring to FIGS. 3A to 3G, a segment of the tube 110 of the propulsiondevice 100 is shown according to some embodiments, illustrating thecavitation process in a series of diagrams. The cavitation process issimilar to that described in relation to FIGS. 2A to 2F; however, thetube 110 shown in FIGS. 3A to 3G also includes one or more mechanisms330 configured to promote cavitation, bubble nucleation and/or bubblecoalescence in one or more regions of the channel 120 when the pressureis reduced.

Referring to FIG. 3A, at the base pressure, the channel 120 may besubstantially or entirely filled with the liquid 130, with little or nogas within the channel 120.

When the pressure in the channel 120 is gradually reduced by thepressure actuator 140, gas bubbles 133 may begin to form in the liquid130 within the channel 120, as shown in FIG. 3B. Some bubbles 133 mayform randomly throughout the liquid 130; however, the likelihood ofbubbles 133 forming will be higher in the regions of thecavitation-promoting mechanisms 330.

As the pressure is reduced further, the bubbles 133 may grow in volumeto form larger bubbles 133 c, as shown in FIG. 3C, and new bubbles 133may continue to be formed through nucleation. Some of the bubbles 133,133 c may coalesce to form even larger bubbles 133 d, as shown in FIG.3D.

The bubbles 133 may coalesce to form lumen-spanning bubbles 133 e whichspan the entire diameter of a lumen of the channel 120, as shown in FIG.3E. The formation of lumen-spanning bubbles 133 e may be more likely inthe regions of the mechanisms 330 due to a greater number or size ofbubbles being formed and/or enhanced bubble coalescence.

When the pressure is increased, the liquid 130 is accelerated in adistal direction (i.e., towards the first or distal end 122 of thechannel 120), as indicated by arrows 301 in FIG. 3F, and the bubbles 133are compressed and reduce in volume, as shown in FIG. 3G.

When the bubbles 133 are compressed, they experience a sudden increasein pressure and density, and collapse (i.e., dissolve and/or condense)back into the liquid 130, as shown in FIG. 3A.

The mechanisms 330 may comprise any suitable means for enhancing,promoting, encouraging or increasing the likelihood of cavitation,bubble nucleation and/or bubble coalescence.

Referring to FIG. 4, in some embodiments, the one or more mechanisms 330may comprise a variation in a thermal conductivity and/or thermal massof a wall 118 of the tube along the length of the channel 120. Thisvariation in thermal conductivity and/or thermal mass could be achievedby including wall portions 430 at different locations along the lengthof the channel 120 comprising a material having a higher thermalconductivity and/or thermal mass than the rest of the wall 118. Forexample, in some embodiments, the wall 118 may be formed of an extrudedpolymer, and metal particles could be impregnated in certain portions ofthe wall 118 to create the wall portions 430 of relatively higherthermal mass and thermal conductivity.

The difference in thermal conductivity and/or thermal mass between thewall portions 430 and the rest of the wall 118 may result in a higherlikelihood of cavitation and bubble nucleation in the region of the wallportions 430 compared with the rest of the channel 120.

In some embodiments, the thermal conductivity of the wall 118 may varyalong the length of the channel over a range of about 0.25 Wm⁻¹ K⁻¹ to240 Wm⁻¹ K⁻¹. In some embodiments, the thermal conductivity of the wallportions 430 may be higher than the rest of the wall 118 by a factor ofat least 10, at least 100, at least 500, or at least 1000. For example,in some embodiments, the thermal conductivity of the wall portions 430may be in the range of about 100 Wm⁻¹ K¹ to 300 Wm⁻¹ K¹, about 150 Wm⁻¹K⁻¹ to 250 Wm⁻¹ K⁻¹, or about 200 Wm⁻¹ K⁻¹, while the thermalconductivity of the rest of the wall 118 may be in the range of about0.1 Wm⁻¹ K¹ to 10 Wm⁻¹ K⁻¹, or about 0.5 Wm⁻¹ K⁻¹ to 1 Wm⁻¹ K⁻¹.

Referring to FIG. 5, in some embodiments, the one or more mechanisms 330may comprise one or more acoustic transducers 530. The acoustictransducers 530 may be connected to a controller via one or more cables535 and configured to emit acoustic energy with an amplitude andfrequency which promotes cavitation, bubble nucleation and/or bubblecoalescence.

The acoustic transducers 530 may be coupled to the external or internalsurface of the tube 110, disposed outside of the 118 wall of the tube110, or in some embodiments, may be disposed or embedded within the wall118 of the tube 110. In some embodiments, the acoustic transducers 530may comprise piezoelectric patch transducers.

An operating frequency of the acoustic transducers 530 may be in therange of about 1 kHz to 100 kHz or about 10 kHz to 25 kHz, for example.The operating frequency of the acoustic transducers 530 may be selectedto be higher than the Blake threshold for the mechanical nucleation ofgas bubbles of at least 1 micrometre in systems with a gas saturationcoefficient approaching 1 (i.e fully saturated). The threshold increaseswith increasing frequency and decreasing gas saturation (for reference,see Acoustic cavitation prediction, R. E. Apfel, The Journal of theAcoustical Society of America 69, 1624 (1981).)

Acoustic insonation energy may be directed into a lumen of the channelby the acoustic transducers 530 to promote, enhance or assist ininducing cavitation in the liquid 130. In some embodiments, thecharacteristics of the insonation field may comprise: a pressurevariation in the range of about 10 MPa to 100 Mpa, a pulse duration inthe range of about 0.2 ms 10 ms, and a total power in the range of about10 mW to 100 mW, for example. In some embodiments, the acoustictransducers 530 may be operated with a pressure of about 100 kPa, adisplacement of about 25 μm and a frequency of about 21 kHz.

In some embodiments, the mechanisms 330 may comprise one or more lasersconfigured to induce cavitation in the liquid 130. For example, in someembodiments, the mechanisms 330 may comprise microdiode laser modulesembedded in the wall 118 of the tube 110. The laser modules may beactivated in a pulse of 10 ms to 20 ms duration to co-inside with thelow pressure phase of the pressure cycle, to promote, enhance or assistin inducing nucleation of gas bubbles 133.

In some embodiments, the mechanisms 330 may comprise one or more pairsof electrical conductors disposed within the lumen of the channel 120and arranged with a close separation in the range of about 0.1 mm to 0.5mm, such that an electrical current can discharge from one conductor tothe other through the liquid 130 causing ionisation of the liquid 130and subsequent gas nucleation. The conductive pairs may be arranged in acircular configuration and imbedded in the wall of the non-conductivepolymer tube. The conductive pairs may be connected to an electricalpower source via conductive wires running along the length of the tube110. The power source may comprise a high capacity, high voltage, lowcurrent discharge circuit which can be timed to discharge at the lowestpoint of the pressure cycle produced by the pressure actuator 140. Thesupplied voltage may be in the range of about 100V to 200V. The currentmay be in the range of about 1 mA to 10 mA.

Referring to FIG. 6, in some embodiments, the one or more mechanisms 330may comprise a surface variation 630 on the internal surface 126 of thetube 110. That is, a surface variation portion 630 of the internalsurface 126, which is different to the rest of the internal surface 126and configured to promote or encourage bubble nucleation.

In some embodiments, the surface variation 630 may comprise a coatingapplied to part of the internal surface 126 of the tube 110. In someembodiments, the surface variation 630 may comprise a coating of acatalytic material, such as octadecyltrichlorosilane (for promoting CO₂nucleation) or other similar compounds, for example. In someembodiments, the surface variation 630 may comprise a hydrophobiccoating, such as silane (silicone hydride) compounds, Parylene C, orflouropolymers such as PTFE (Teflon™), manganese oxide polystyrene(MnO2/PS), nano-composite zinc oxide polystyrene (ZnO/PS),nano-composite precipitated calcium carbonate or fluorinated acrylateoligomers, for example.

In some embodiments, the rest of the internal surface 126 may be formedof or coated with a hydrophilic material, such as urethane, acrylic,polyvinylpyrrolidone (PVP), polyethylene oxide, combinations ofhydroxyethylmethacrylate, or acrylamides, for example, or anothermaterial suitable for discouraging bubble nucleation on the rest of theinternal surface 126 (i.e. away from the surface variations 630).

In some embodiments, the surface variation 630 may comprise atopographical variation. Relatively small topographical variations(e.g., at length scales in the order of 1 μm-100 μm) may providenucleation sites to encourage or promote bubble nucleation and growth.For example, the topographical variation may comprise a change insurface roughness, a microporous surface, a scratched or pitted surface,a plurality of protrusions, projecting fibres, nanotubes, pits,channels, ridges, fins, recesses, cavities or other geometricalvariation. The topographical variations may be formed by moulding,scratching, cutting, knurling, etching, abrasion, or impression, forexample. In some embodiments, porous particulates such as ceramics maybe embedded in the wall 118 of the tube 110 at the inner surface 126 toprovide nucleation sites.

In some embodiments, the topographical variation may extend across theentire internal surface 126 of the tube 110. In some embodiments, thetube 110 may be formed with the topographical variation extending acrossthe entire internal surface 126, and then certain portions of theinternal surface 126 may be smoothed (for example, with a polymercoating), leaving the exposed/unsmoothed portions of the topographicalvariation to form the surface variations 630. For example, the wall 118of the tube 110 may be formed of a porous material, and then certainportions of the inner surface 126 may be sealed leaving theexposed/unsealed portions of the inner surface 126 to form the surfacevariations 630.

The surface variations 630 may comprise any suitable topographicalvariations for a given application. A number of suitable topographicalvariations are described below.

In some embodiments, the topographical variation may define a pluralityof V-shaped channels. The V-shaped channels may be aligned in parallelwith each other, or may be randomly oriented and intersect each other.

A characteristic angle of the V-shaped channels (i.e., the angle of theapex of the V-shape) may be in the range of about 10° to 90°, about 30°to 60°, or about 40° to 50°, for example. An average width of theV-shaped channels may be in the range of about 1 μm to 10 μm, or about 2μm to 4 μm, for example. An average depth of the V-shaped channels maybe in the range of about 1 μm to 10 μm, or about 2 μm to 4 μm, forexample.

Referring to FIG. 7, in some embodiments, a surface variation 730 maycomprise a partially randomised pattern of intersecting V-shapedchannels 737. This may be achieved by abrasion using Diamondparticulates with a nominal size of 2 μm. The Diamond particulates mayhave sharp V-shaped vertices and may be sintered on to a metal rod forrotary application to the internal surface 126. The metal rod may beapplied to the internal surface 126 with a rotary oscillation to producethe surface variations 730. An Atomic Force micrograph of a typicalrandom V-shaped scratch pattern achieved using this method is shown inFIG. 7.

In some embodiments, the topographical variation may define a pluralityof conical pits. The conical pits may be arranged randomly or in aperiodic array.

A characteristic angle of the conical pits (i.e., the angle of the apexof the conical pits) may be in the range of about 10° to 90°, about 30°to 60°, or about 40° to 50°, for example. An average width of theconical pits may be in the range of about 1 μm to 10 μm, or about 2 μmto 4 μm, for example. An average depth of the conical pits may be in therange of about 1 μm to 10 μm, or about 2 μm to 4 μm, for example.

In some embodiments, the topographical variation may define a pluralityof protrusions. The protrusions may define any suitable shape and, insome embodiments, may define a plurality of different shapes. Theprotrusions may be arranged randomly or in a periodic array.

An average height of the protrusions may be in the range of about 0.1 μmto 1 mm, about 1 μm to 500 μm, or about 10 μm to 100 μm, for example. Anaverage width of the protrusions may be in the range of about 0.1 μm to500 μm, about 0.5 μm to 100 μm, or about 1 μm to 10 μm, for example. Anaverage distance between adjacent protrusions may be in the range ofabout 0.1 μm to 500 μm, about 0.5 μm to 100 μm, or about 1 μm to 10 μm,for example.

Referring to FIGS. 8A to 8E, some examples of surface variations 830 areshown according to some embodiments. The surface variations 830 eachdefine a plurality of protrusions 835. In some embodiments, theprotrusions 835 may define fins or ridges 835 separated by channels 837.

In some embodiments, the protrusions 835 may comprise nanowires orhollow nanotubes which may be formed of materials such as carbon orsilicon, for example. For nanowire, the width of the protrusions 835 maybe in the range of about 10 nm to 500 nm, about 20 nm to 300 nm, orabout 100 nm to 200 nm; the length or height of the protrusions 835 maybe in the range of about 0.1 μm to 100 μm, about 1 μm to 50 μm, or about10 μm to 20 μm; and the average spacing between protrusions 835 may bein the range of about 10 nm to 10 μm, about 10 nm to 100 nm, or about100 nm to 1 μm, for example. For nanotubes, the width of the protrusions835 may be in the range of about 10 nm to 100 nm, about 10 nm to 50 nm,or about 20 nm to 40 nm; the length or height of the protrusions 835 maybe in the range of about 1 μm to 50 μm, about 5 μm to 30 μm, or about 10μm to 20 μm; the pore size (or internal diameter) of the protrusions 835may be in the range of about 1 μm to 40 μm, about 5 μm to 30 μm, orabout 10 μm to 20 μm; and the average spacing between protrusions 835may be in the range of about 10 nm to 10 μm, about 10 nm to 100 nm, orabout 100 nm to 1 μm, for example.

In some embodiments, the topographical variation may define a poroussurface, such as a foam, sintered material or other porous material, forexample. An average pore size of the porous surface may be in the rangeof about 10 nm to 200 μm, about 20 nm to 250 nm, about 50 nm to 150 nm,about 10 μm to about 200 μm, or about 50 μm to about 100 μm, forexample. The porous surface may comprise a layer of porous material. Thethickness of the porous layer may be in the range of about 10 μm to 1mm, or about 50 μm to 100 μm, for example.

Referring to FIG. 9, a surface variation 930 comprising a porous layer933 is shown according to some embodiments. The porous layer 933 may beformed of sintered particles 935 with diameters ranging from about 10 μmto about 100 μm, for example.

In some embodiments, the topographical variation may have a surfaceroughness in the range of about 0.1 μm to 500 μm, about 0.5 μm to 100μm, or about 1 μm to 10 μm, for example.

In some embodiments, one or more additives may be included in the liquid13—to promote cavitation, bubble nucleation and/or bubble coalescence.For example, additives may be included to alter the density, viscosity,pH-level, gas solubility, coalescence characteristics or surface tensionof the liquid 130.

The solubility and coalescence characteristics of each fluid gascombination may be dependent on factors which may be controlled, such astemperature and pH. In the case of CO₂, it is thought that the pH of thesolution should ideally be adjusted to be between 6 and 6.5 for optimumeffect. If the pH is above 6.5 it may be difficult to induce bubblenucleation due to the high solubility of the gas in water. In someembodiments, where CO₂ is used as the gas, the pH of the solution may bedecreased to a level between 6 and 6.5 with the addition of acetic acidproducing to promote nucleation and coalescence of CO₂ bubbles in theliquid.

In some applications, the mechanical work of the pressure actuator 140acting on the liquid 130 may produce heating of the liquid 130, whichmay decrease the solubility of the gas 133 in the liquid 130. In someembodiments, the propulsion device 100 may include a heat sink (notshown) to draw excess heat away from the liquid 130. For example, theheat sink may comprise a metal heat sink disposed at or near theproximal end 114 of the tube 110, which may be disposed within oradjacent to the pressure actuator 140. The heat sink may be cooled byair convection, refrigeration, or radiation.

In some embodiments, the thermal conductivity of the liquid 130 may besufficient for heat to be transferred through the liquid 130 along thetube 110 to the heat sink. In some embodiments, salts such as PotassiumFormate may be added to water to increase the thermal conductivity anddensity of the liquid 130 without significantly increasing the viscosityor boiling point.

In some embodiments, the thermal mass and conductivity of the tube 110itself may be sufficient for heat to be transferred along the tube 110to the heat sink. In some embodiments, the tube wall 118 may compriseone or more heat conductors, such as a metallic film or wire, totransfer heat along the tube 110 to the heat sink.

In some embodiments, the liquid 130 may comprise a particularly denseliquid and/or one or more additives may be included in the liquid 130 toincrease the density or inertia of the liquid 130 in order to increasethe momentum developed when the liquid 130 is accelerated and thus toincrease the momentum transferred to the tube 110 to progress the tube110 along the passage.

In some embodiments, such as for medical use, the liquid 130 maycomprise water combined with one or more additives, such as: ethanol toreduce surface tension and viscosity; citric acid or acetic acid toreduce the pH-level; or salts such as sodium chloride to increase thedensity.

In some embodiments, the internal surface 126 of the tube 110 may definea relatively large scale topographical variation (for example, withlength scales in the range of about 5% to 10% of the internal diameterof the tube 110) configured to enhance momentum transfer from the liquid130 to the tube 110 during the sudden pressure increase.

Referring to FIGS. 10A to 10C, segments of tube 110 are shownillustrating some examples of large scale topographical variationsdefined by the internal surface 126, according to some embodiments. Theinternal surface 126 may define a plurality of periodic annular ridges1010 swept back in a proximal direction (towards the second or proximalend 124 of the channel 120). The ridges 1010 appear as a swept fir treepattern, or proximally swept teeth in cross-section as shown in FIGS.10A to 10C.

The proximally swept annular ridges 1010 may provide a fluid diodeeffect, whereby there is a greater resistance to fluid flow in thedistal direction and relatively less resistance to fluid flow in theproximal direction. This effect may enhance momentum transfer from theliquid 130 to the tube 110 during the sudden pressure increase.

In some embodiments, the annular ridges 1010 may not be proximallyswept, and a fluid diode effect may be achieved with a different type oftopographical variation or, in some embodiments, not at all.

As described above, when the channel 120 accommodates a volume of liquid130 and a separate volume of gas 133 in an initial or rest state, thepressure actuator 140 may be configured to increase the channel pressureto dissolve the gas 133 into the liquid 130 (this may be referred to asa pressure increase phase), and subsequently decrease the channelpressure to induce nucleation and cavitation of gas bubbles 133 in theliquid 130 (this may be referred to as a pressure decrease phase).Alternatively, when the channel 120 accommodates only the liquid 130 inthe initial or rest state, the pressure actuator 140 may be configuredto decrease the channel pressure to induce nucleation and cavitation ofgas bubbles 133 in the liquid 130 (the pressure decrease phase), andsubsequently increase the channel pressure to collapse the gas bubbles133 (through condensation or dissolution) into the liquid 130 (thepressure increase phase).

In some embodiments, the pressure increase phase may be substantiallysimilar in duration to the pressure decrease phase. In some embodiments,the duration of the pressure increase phase may be significantly shorterthan the duration of the pressure decrease phase.

In some embodiments, the pressure actuator 140 may be configured toincrease the pressure over a period of time which is between about 1%and 50% of a period of time over which the pressure is reduced,optionally between about 5% and 30%, optionally between about 10% and20%, for example.

As described above, the pressure actuator 140 may comprise any suitableapparatus for varying the channel pressure in the manner described. Insome embodiments, the pressure actuator 140 may comprise a flexiblediaphragm with a mechanism configured to deflect or deform the diaphragmto change the volume of the system and control the channel pressure. Insome embodiments, the pressure actuator 140 may comprise a reciprocatingpiston driven by a motor, such as an electric motor or linear motor, forexample.

Referring to FIG. 11, an exemplary displacement profile x(t) andcorresponding velocity profile v(t) are shown illustrating the movementof the pressure actuator 140, in the form of a piston, over time,according to some embodiments.

The displacement and velocity profiles show a pressure increase phase1110 followed by a pressure decrease phase 1120. During the pressureincrease phase 1110 (corresponding to a compression stroke of thepiston), the piston undergoes a rapid acceleration 1112 which is madepossible by the highly compressible nature of the gas bubbles 133.

Once the gas bubbles 133 collapse back into the liquid 130, there is asudden deceleration 1114 of the piston due to the relativelyincompressible nature of the liquid 130 (i.e., greatly less compressiblethan the gas 133). The sudden deceleration 1114 of the piston and liquid130 results in a large impulse and transfer of momentum from the liquid130 to the tube 110 and a consequent propulsive effect which acts toprogress the tube 110 along the passage 103.

After the deceleration 1114 of the piston, once the channel pressure hasreached a maximum the pressure decrease phase 1120 begins as the pistonis withdrawn. The withdrawal stroke (pressure decrease phase 1120) maybe significantly slower than the compression stroke (pressure increasephase 1110) due to the time required for nucleation and cavitation ofthe gas bubbles 133 to occur. The channel pressure is then decreased toa minimum. The movement of the piston may then be repeated in a similarmanner to repeat the pressure variation cycle.

The pressure actuator 140 may be configured to repeatedly increase anddecrease the channel pressure to impart momentum to the tube 110 withmultiple impulses, each impulse being associated with correspondingpressure increase phases. In some embodiments, the channel pressure maybe varied by the pressure actuator 140 in a periodic or cyclic mannerwith a repeating pressure cycle (i.e., pressure increase followed bypressure decrease). In some embodiments, the pressure actuator 140 maybe configured to vary the channel pressure according to a repeatingpressure cycle with a frequency in the range of about 0.1 Hz to 10 Hz,about 0.5 Hz to 5 Hz, about 0.5 Hz to 1.5 Hz, about 2 Hz to 4 Hz, orabout 3 Hz, for example.

In some embodiments, the pressure actuator 140 may be configured tooperate in a reverse cycle to adjust the channel pressure to impart areverse impulse to the tube 110 to move the instrument in a proximaldirection. This reverse pressure cycle may be used to withdraw theinstrument from the passage.

Referring to FIG. 12, an exemplary pressure/time profile is shown,according to some embodiments, illustrating the changes in channelpressure required to compress the gas bubbles 133 into the liquid 130when the pressure is increased, and subsequently induce cavitation ofgas bubbles 133 in the liquid 130 when the pressure is reduced. Thepressure scale is shown in kilopascals (kPa) above atmospheric pressureand the time scale is shown in seconds. The channel pressure is reducedgradually over a period of about 0.3 s, and then suddenly increased overa period of about 0.05 s. This pressurisation cycle is repeated at afrequency of about 3 Hz.

As discussed previously, in some embodiments, it may be desirable forthe channel 120 to be relatively small in order to increase thelikelihood of spanning bubbles 133 e forming before compression. Theinternal diameter of the channel 120 may be in the range of 0.1 mm to 10mm, 0.1 mm to 1 mm, 0.1 mm to 0.5 mm, 1 mm to 7 mm, or 2 mm to 5 mm, forexample. In some embodiments, the propulsion device 100 may comprise aplurality of the tubes 110 extending side by side as illustrated by thecross-sections of example tube configurations shown in FIGS. 13A and13B.

In some embodiments, the tubes 110 may be arranged around an instrumentchannel 1301 configured to receive a probe such as an endoscope, forexample as illustrated in FIG. 13B. In some embodiments, the tubes 110may be arranged in a bundle for insertion into a lumen of a probe suchas an endoscope, for example as illustrated in FIG. 13A. In someembodiments, the tubes 110 may be integrally formed as part of a probesuch as an endoscope, with instrument channels (e.g. video tract,lighting, irrigation, suction, steering, biopsy and other instrumentchannels) extending alongside the tubes 110.

In some embodiments, the propulsion device 100 may comprise a first tube110 within a second tube 110, with the liquid 130 and gas 133 containedin an annular channel 120 defined between the two tubes 110. An innerlumen of the first tube 110 may also contain liquid 130 and gas 133, oralternatively, in some embodiments, the inner lumen of the first tube110 may define an instrument channel.

The tube 110 or tubes 110 may be formed of a flexible material withsufficient strength and stiffness to withstand the expected forces for agiven application. For medical applications, some suitable materials maycomprise: high to ultra-high molecular weight polyethylene or otherbiocompatible polymers, for example. In some embodiments, the tube 110or tubes 110 may be formed of composite materials, such as apolyethylene spiral with polyurethane and silicone elastomer coatings,for example.

The dimensions of the tubes 110 may vary for different applications. Forexample, for a medical endoscope, such as a gastro-intestinal endoscope,a single tube propulsion device may comprise a tube 110 with an externaldiameter of 8 mm and an internal diameter of 6 mm, or an externaldiameter of 6 mm and an internal diameter of 4.5 mm, whereas amulti-tube propulsion device may comprise 4 tubes 110, each having anexternal diameter of 3 mm and an internal diameter of 2 mm. In someembodiments, the tube 110 of a single tube propulsion device 100 or thetubes 110 of a multi-tube propulsion device 100 may have an internaldiameter in the range of 1 mm to 5 mm, for example, and an externaldiameter in the range of 0.5 mm to 15 mm, 1 mm to 10 mm, 2 mm to 8 mm or4 mm to 6 mm, for example. The lengths of medical endoscopes aretypically in the range of about 1 m to 5 m, or about 3 m to 4 m, forexample. In some embodiments, such as for gastro-intestinal endoscopy,the tube(s) 110 may have a length in the range of 3 m to 4 m, 1 m to 5m, or even greater than 5 m, such as 5 m to 15 m, or 7 m to 9 m, forveterinary applications, for example. In some embodiments, such as forarterial endoscopy, the tube(s) may have a length in the range of 0.5 mto 2 m, 0.7 m to 1.5 m or 0.9 m to 1.2 m, for example. In someembodiments, such as for industrial endoscopes, the dimensions of thetubes may be much larger.

For medical applications, it will usually be important for thepropulsion device 100 to be sterile. To that end, it may be desirablefor at least part of the device 100 to comprise a disposable componentwhich can be provided in a sterile package and discarded after use.Referring to FIG. 14, a propulsion device 1400 is shown according tosome embodiments. The propulsion device 1400 comprises generally similarfeatures to those described in relation to propulsion device 100 and arereferred to with like numbers. A pressure actuator 1440 and proximal end1414 of a tube 1410 defining a channel 1420 are shown. It will beunderstood that the tube 1410 extends to a distal end (not shown) asdescribed in relation to the propulsion device 100 of FIG. 1. The tube1410 may be referred to as a propulsion tube, and may comprise similarfeatures to tube 110 described above. In some embodiments, tube 1410 maycomprise tube 110, or a bundle of tubes 110 as described in relation toFIG. 13A or 13B.

The pressure actuator 1440 comprises a housing 1442, a driving mechanism1444 (in the form of a motor), an actuation rod 1446 and a socket 1448defined in a side of the housing 1442. The pressure actuator 1440further comprises a piston assembly 1450 comprising a body 1452 defininga cylinder 1454, a piston 1456 disposed in the cylinder, and a pistonseal 158 to seal the piston 1456 against an internal bore 1460 of thecylinder 1454. The piston 1456 and cylinder 1454 act together to form apiston pump. However, in some embodiments, a different type of pump orcompressor may be used to adjust the channel pressure in the tube 1410,for example, a diaphragm pump, as described below in relation to FIG.17.

The piston assembly 1450 is attached to the tube 1410 to form a tubeunit 1401. The tube unit 1401 may be manufactured and filled with apredetermined mass of liquid 130 and a predetermined mass of gas 133sealed within the channel 1420 of the tube 1410 at a predeterminedpressure. The tube unit 1401 may then be packaged and sterilisedseparately from the housing 1442 (including the socket 1448 and drivingmechanism 1444) so that the housing 1442 can be resterilised and reused,while the tube unit 1401 can be manufactured and sterilised as adisposable unit to be discarded after use.

This arrangement may make it easier to sterilise the fluid 130, 133 andtube unit 1401 together rather than having to fill the tube 1410 withsterile fluid 130, 133 in a sterile environment such as an operatingtheatre.

The piston assembly 1450 is removably coupled to the housing 1442 (i.e.,removable from the socket 1448). The socket 1448 may comprise aninternal cylindrical wall 1486 that helps define the socket 1448 andaccommodate the piston assembly 1450 in the socket 1448.

The body 1452 defines a first opening 1462 and a second opening 1464with the cylinder 1454 defining an open passage between the first andsecond openings 1462, 1464. The proximal end 1414 of the tube 1410 isconnected to the body 1452 of the piston assembly 1450 at the secondopening 1464, such that the channel 1420 is in fluid communication withthe cylinder 1454. The internal diameter or bore of the cylinder 1454may be significantly larger than the internal diameter of the tube 1410so that a relatively shorter stroke length is required to affect thedesired pressure changes in the tube 1410. For example, the ratiobetween the internal diameters of the tube 1410 and the cylinder 1454may be in the range of 0.01 to 0.5, 0.05 to 0.4, 0.1 to 0.3, or 0.1 to0.2.

The internal diameter of the cylinder 1454 may gradually taper down tothe internal diameter of the tube 1410 at the second opening 1464. Insome embodiments, the second opening 1464 may be offset from a centralaxis of the body 1452, and may be disposed at or near a top of thecylinder 1454 when the pressure actuator 1440 is disposed in ahorizontal configuration. This may reduce the likelihood of gas bubbles,which may be formed in the cylinder 1454 during cavitation, beingtrapped in the cylinder, and instead, allow the bubbles to rise uptowards the second opening 1464 and into the tube 1410 due to gravity.

The pressure actuator 1440 is configured to move the piston 1456 backand forth along the length of the cylinder 1454 to adjust the channelpressure, such as by varying the channel pressure in the tube 1410. Acompression stroke, or pressure increase stroke, moves the piston 1456towards the tube 1410 and pushes fluid from the cylinder 1454 and intothe tube 1410, thereby increasing the channel pressure in the tube 1410.A return stroke, or withdrawal or pressure decrease stroke, moves thepiston 1456 away from the tube 1410 and allows fluid to flow back intothe cylinder 1454 from the tube 1410, thereby decreasing the channelpressure in the tube 1410.

The motor 1444 and actuation rod 1446 are disposed in the housing 1442,such that when the piston assembly 1450 is disposed in the socket 1448,the actuation rod 1446 is aligned with the first opening 1462 of thebody 1452 and can pass through the first opening 1462 to contact andmove the piston 1456 within the cylinder 1454. In some embodiments, thechannel pressure within the tube 1410 may be sufficient to move thepiston 1456 through the return stroke when the actuation rod 1446 iswithdrawn from the cylinder 1454. In some embodiments, the pistonassembly 1450 may further comprise a biasing member 1470, such as aspring, to bias the piston 1456 against the actuation rod 1446 and/oraway from the tube 1410, such that the piston 1456 is pushed backthrough the return stroke by the biasing member 1470 when the actuationrod 1446 is withdrawn from the cylinder 1454. For example, the biasingmember 1470 may comprise a stainless steel spring and/or a helicalspring. In some embodiments, the actuation rod 1446 may be removablycouplable to the piston 1456 itself to allow the actuation rod 1446 topull the piston 1456 back as well as pushing the piston 1456 forward.

The piston assembly 1450 may further comprise a locking ring 1466 torestrict the piston 1456 from being removed from the cylinder 1454through the first opening 1462. In some embodiments, the drivingmechanism 1444 may comprise one or more electromagnets configured todrive the piston 1456 directly rather than via a motor and actuationrod.

The body 1452 may further define one or more locking lugs 1468configured to engage the socket 1448 to couple the piston assembly 1450to the housing 1442. The socket 1448 may also comprise one or moreexternal flanges 1488 configured to engage the lugs 1468 to secure thepiston assembly 1450 in the socket 1448. In this way, the pistonassembly 1450 is configured to be removably coupled to the housing 1442,such that the piston assembly 1450 and tube 1410 can be manufacturedtogether as a single disposable tube unit, while the housing 1442 andmotor 1444 can be reused with a new tube unit for each new operation.The locking lugs 1468 may alternatively be referred to as tabs or radialprojections, for example.

The tube unit may be assembled with liquid 130 and gas 133 disposed inthe channel 1420 (either at atmospheric pressure or at a higher pressuredepending on the application) and connected to the piston assembly 1450to seal liquid 130 and gas 133 within the tube unit. In someembodiments, the body 1452 may be fixed to the proximal 1414 end of thetube 1410 and the piston 1456 subsequently placed in the cylinder 1454and locked in with the locking ring 1466 to seal the liquid 130 and gas133 in the channel 1420 and cylinder 1454. The seal 1458 may compriseone or more gaskets such as o-rings, which may be seated in one or morecorresponding gasket seats defined in the piston 1456, or alternativelyin the inner surface of the cylinder 1454.

In some embodiments, the body 1452 of the piston assembly 1450 mayinclude an inlet valve 1490 for filling cylinder 1454 and the channel1420 of the tube 1410 with a predetermined mass of a selected liquid 130and a predetermined mass of a selected gas 133. The body 1452 may alsoinclude an outlet valve 1492 to allow air to be released from thechannel 1420 and cylinder 1454 while they are being filled with theliquid 130 and gas 133.

The valves 1490, 1492 may be located at one end of the body 1452 nearthe second opening and may be configured to maintain pressure within thecylinder 1454 and channel 1420. In some embodiments, the valves 1490,1492 may comprise spring plunger valves. The inlet valve 1490 may belocated relatively nearer the second opening 1464 and the outlet valve1492 may be located relatively farther from the second opening 1464, asshown in FIG. 14.

To fill the tube unit 1401 with the gas 133 and liquid 130, the body1452 may be held upside down, or arranged with the valves 1490, 1492disposed above the second opening, with most or substantially all of thevolume of the channel 1420 and cylinder 1454 at a lower level than theoutlet valve 1492. This is to encourage excess air to rise towards theoutlet valve 1492 when the channel 1420 and cylinder 1454 are beingfilled with the liquid 130. The air may be sucked from the outlet valve1492 via a vacuum line or other suction.

In some cases, the liquid 130 and gas 133 may be mixed together in apressure vessel, such that the gas 133 is fully dissolved in the liquid130 in a saturated solution, in which case the gas/liquid solution canbe introduced to the tube unit 1401 via the inlet valve 1490 as the airis removed via the outlet valve 1492. If the gas 133 and liquid 130 areto be introduced separately, it may be preferable to first remove asmuch air as possible from the channel 1420 and cylinder 1454 via theoutlet valve 1492; before injecting the liquid 130 into the channel 1420and cylinder 1454 via the inlet valve 1490; removing any remaining airvia the outlet valve 1492; and then injecting the gas 133 into thechannel 1420 and cylinder 1454 via the inlet valve 1492.

Alternatively, the tube 1410 could be formed with an open distal end;the liquid 130 and gas 133 could be drawn along the channel 1420 andinto the cylinder 1454 as the air is withdrawn from the cylinder 1454;and then the distal end of the tube 1410 could be closed with a plug andsteel swage to hold the plug in the channel 1420 and seal the tube 1410.However, it may be preferable to form the tube 1410 with a closed distalend to avoid having to close it with a plug or other means.

Once the tube unit is fully assembled with the liquid 130 and gas 133sealed inside the channel 1420 and cylinder 1454, the tube unit may bepackaged and sterilised with gamma radiation, for example. Together, thetube 1410 and piston assembly 1450 may define a sealed vessel containinga selected mass of liquid 130 and a selected mass of gas 133. In someembodiments, a gas tight closure may be fitted to the body 1452 of thepiston assembly 1450 during packaging to close the first opening 1462 ofthe cylinder 1454 and to assist in maintaining a selected tube channelpressure until use. The body 1452 may comprise an engaging portion (notshown) defining one or more recesses, notches or projections to engagethe closure and form a gas tight seal.

In some embodiments, the pressure actuator 1440 may comprise a diaphragmpump instead of a piston pump to control the channel pressure in thetube 1410. Referring to FIG. 17, the propulsion device 1400 is shownwith an alternative tube unit 1701, comprising a diaphragm pump assembly1750 instead of the piston assembly 1450 described above. In all otherrespects, the tube unit 1701 may be substantially similar to the tubeunit 1401 described above with similar features indicated with likereference numerals.

The diaphragm pump assembly 1750 comprises a body 1752 defining achamber 1754 extending between a first opening 1762 and a second opening1764, and a diaphragm 1770 which closes or covers the first opening 1762of the chamber 1754. The proximal end 1414 of the tube 1410 is connectedto the body 1752 of the diaphragm pump assembly 1750 at the secondopening 1764, such that the channel 1420 is in fluid communication withthe chamber 1754. The body 1752 may further define one or more lugs 1768configured to engage the flanges 1488 of the socket 1448 to couple thediaphragm pump assembly 1750 to the housing 1442.

In some embodiments, the body 1752 of the diaphragm pump assembly 1750may include an inlet valve 1790 and outlet valve 1792, which may beconfigured in a similar manner to valves 1490 and 1492 as described inrelation to tube unit 1401 and body 1452.

The diaphragm 1770 may be formed separately and held in place over thefirst opening 1762 of the chamber 1754 by a clamp 1772. For example, theclamp 1772 may comprise a threaded locking ring configured to threadedlyengage the body 1752 thereby clamping a periphery of the diaphragm 1770between the body 1752 and the clamp 1772, as shown in FIG. 17. In otherembodiments, the diaphragm 1770 may be integrally formed with the body1752, for example, using a composite moulding process.

The diaphragm 1770 comprises a resiliently deformable membrane which maybe deformed by an actuator to change the volume of the chamber 1754 influid communication with the channel 1420 of the tube 1410. A centralportion 1774 of the diaphragm 1770 may be removably coupled to theactuation rod 1446 of the driving mechanism 1444. The diaphragm 1770includes a resiliently deformable portion 1776 surrounding the centralportion 1774 allowing the central portion 1774 of the diaphragm to bemoved back and forth relative to the body 1752 along an axis 1780 whichis substantially normal (perpendicular) to a surface of the centralportion 1774. For example, parallel to or in alignment with the axialmotion of the actuation rod 1446 of the driving mechanism or linearmotor 1444.

As the central portion 1774 of the diaphragm 1770 moves back and forthbetween a compressed position 1778 a (shown in dashed lines) and awithdrawn position 1778 b (shown in solid lines), the volume of thechamber 1754 is changed. Thus, the channel pressure in the tube 1410 canbe adjusted and controlled by controlling the position of the actuationrod 1446 and central portion 1774 of the diaphragm 1770.

The diaphragm 1770 may be round or rotationally symmetric, but coulddefine any suitable shape for a resiliently deformable membrane. Thechamber 1754 is illustrated as a cylinder in FIG. 17, but may define anysuitable shape for providing the desired range of channel pressure. Insome embodiments, the chamber 1754 may be relatively short and tapertowards the second end 1764 allowing for a relatively wide diaphragm1770 and relatively narrow diameter of the second opening 1764, to allowa greater range of channel pressures for relatively little axialmovement of the diaphragm.

In some embodiments, different tube units for different medicalapplications may be fitted with similar piston assemblies to allow eachof the different tube units to be used with a common housing 1442 andmotor 1444. In some embodiments, a plurality of tubes 1410 may beconnected to a single piston assembly 1450 with the channel 1420 of eachtube 1410 being in fluid communication with the cylinder 1454 of thepiston assembly 1450.

In some embodiments, the housing 1442 may comprise a drive console ordrive unit 1500 as shown in FIG. 15. The drive console 1500 may comprisea power switch 1502 to control the supply of power to the drive console1500 from a power source 1560.

The socket 1448 may comprise one or more circumferential flanges 1488extending part way around a circumference of the socket and extendingradially inward to retain the lugs 1468 of the body 1452 in the socket1448. The lugs 1468 are shown in dashed lines in FIG. 15, projectingradially away from the body 1452 to be accommodated within or under theflanges 1488. The lugs 1468 also extend circumferentially around part ofthe body 1452.

Both the lugs 1468 and flanges 1488 are arranged such that there aregaps between the flanges 1488 to allow passage of the lugs 1468 and gapsbetween the lugs 1468 to allow passage of the flanges 1488 when couplingor decoupling the piston assembly 1450 to or from the socket 1448. Tocouple the piston assembly 1450 to the housing 1442, the body 1452 isinserted into the socket 1448 with the lugs 1468 aligned with the gapsbetween the flanges 1488, then the body 1452 is rotated to engage thelugs 1468 in a snug fit in a space defined between the flanges 1488 anda surface (not shown) of the housing 1442 that is opposed to anddirectly underlies the flanges 1488.

In some embodiments, the lugs 1468 and/or flanges 1488 may comprise aresilient click lock, clip or latch to secure the body 1452 againstrotation in the connected alignment with the lugs 1468 engaged with theflanges 1488. The lugs 1468, and/or flanges 1488 may also comprise astopper to restrict rotation of the piston assembly 1450 beyond theangle at which the lugs 1468 are fully engaged with the flanges 1488.

To decouple the piston assembly 1450 from the housing 1442, the body1450 is rotated to disengage the lugs 1468 from the flanges 1488 withthe lugs 1468 aligned with the gaps between the flanges 1488. Then thepiston assembly 1450 can be removed from the socket 1448.

In some embodiments, the body 1450 may comprise an indicator tab 1480 toindicate the correct orientation when coupling the piston assembly 1450to the socket 1448. The flanges 1488 may define a complimentary cut-outor recess 1482 configured to allow passage of the indicator tab 1480when the piston assembly 1450 is correctly oriented for insertion intothe socket 1448. Once inserted into the socket 1448, the body 1450 maybe rotated, with the indicator tab passing under one or more of theflanges 1488, until the lugs 1468 are fully engaged with the flanges1488. In some embodiments, the housing 1442 may comprise an indicia ormarking to indicate the position of the indicator tab 1480 when the lugs1468 are fully engaged with the flanges 1488.

The drive console 1500 may comprise a connection indicator light 1504configured to light up when the piston assembly 1450 is connected to thedrive console 1500. The drive console 1500 may comprise a sensor (notshown) to detect when the piston assembly 1450 is connected to thesocket 1448 and/or when the lugs 1468 are fully engaged with the flanges1488. When the sensor detects connection of the piston assembly 1450 tothe drive console 1500, it may trigger a signal or complete anelectrical circuit to turn on the connection indicator light 1504.

The drive console may comprise an operating indicator light or runningindicator light 1506 configured to light up when the pressure actuator1440 is in operation. The indicator light 1506 may be included in orlinked to an electrical circuit controlling the supply of power to themotor 1444, such that the indicator light 1506 is turned on when themotor 1444 is in operation.

In some embodiments, the drive console 1500 may include a connectionterminal 1508 configured to receive a connector of a signal cable froman external controller, such as a foot switch, for controlling operationof the pressure actuator 1440. In some embodiments, the drive console1500 may include a display or user interface 1510 to provide informationto a user regarding operations of the propulsion device 1400 and/or toallow the user to control operations of the propulsion device 1400. Insome embodiments, the drive console 1500 may comprise a computer and/orcontroller 1550 configured to control operations of the propulsiondevice 1400.

The computer 1550 may be connected to the user interface 1510 to provideinformation about the operations of the propulsion device 1400 and, insome embodiments, may receive inputs from the user interface to selectcertain operating parameters. The user interface 1510 may comprise anintelligent display graphic user interface, and the computer 1550 maycomprise a programmable microprocessor to control functions of the driveconsole 1500 and driving mechanism 1444. The power source 1560 may beconnected to the drive console 1500 and computer 1550, and the computer1550 may control the supply of power to various components of the driveconsole 1500.

Referring to FIG. 16, an endoscopic system 1600 is shown according tosome embodiments. The endoscopic system 1600 comprises an endoscope 1601having an insertion tube 1610 for insertion into a patient; an endoscopeconsole 1620 for controlling operations of the endoscope; an endoscopehandpiece 1630 for further and/or alternative control of operations ofthe endoscope 1601; a propulsion device 1400 for progressing theendoscope 1601 and insertion tube 1610 along a passage within a patient;and a power source (not shown) to supply power to the drive console 1500and endoscope console 1620.

The propulsion device 1400 comprises a propulsion tube 1410 forinsertion into the insertion tube 1610 as described above and a driveconsole 1500 to control operations of the propulsion device 1400.

The endoscopic system 1600 may further comprise a monitor 1640configured to display images received from a camera of the endoscope viathe endoscope console 1620.

The propulsion device 1400 may be operated to provide a propulsive forceto the endoscope 1601 and insertion tube 1610 via momentum transfer inthe propulsion tube 1410, as described above. The propulsive force maybe used to progress the endoscope 1601, insertion tube 1610 andpropulsion tube 1410 along a passage within a patient.

As the momentum is transferred to the propulsion tube 1410 along itslength, there may be a reduced risk of the insertion tube 1610 gettingstuck or reduced resistance as it navigates turns of the passage (e.g.turns of the gastrointestinal tract), as can often occur withconventional push-type endoscopes. This method of propulsion may alsoreduce friction at each turn as the endoscope progresses along thepassage, as it provides an alternative to simply pushing the endoscopeagainst each turn to further progress the endoscope, as is done withconventional push endoscopes.

In some embodiments, the propulsion device 1400 may be able to progressthe endoscope 1601 along the passage at advancement speeds of about 1.5cm/s, for example. Depending on various operational circumstances,conditions, and/or requirements, the advancement speed may be varied inthe range of 0.1 cm/s to 2 cm/s, or 0.5 cm/s to 1 cm/s, for example. Insome applications, the time-pressure profile may be reversed to move thetube 1410 backwards along the passage, for example, to assist inwithdrawing the tube 1410 from the passage. The propulsion device 1400may also allow for an improved completion rate for intestinal endoscopy,by allowing the endoscope 1601 to be progressed further or entirelyalong the length of the intestines to allow the full extent of the smallintestine to be examined. The propulsion device 1400 may also allowaccess to the entire gastro-intestinal tract via endoscopy.

In various embodiments, the propulsion device 100, 1400, 1700 may beconfigured for progressing along a passage any one or more of: aninstrument, probe, sensor, camera, monitoring device, tool, surgicaltool, mining tool, drilling tool, endoscope, enteroscope, duodenoscope,borescope, robot tether, and industrial endoscope, for example. Thepropulsion device 100, 1400, 1700 may be configured to assist inprogressing an instrument, sensor or tool along any one or more of: apassage, mine shaft, well bore, pipe, sewer, wall cavity, and passage ina patient, such as a lumen of a biological passage, artery or tract.

It will be appreciated by persons skilled in the art that numerousvariations and/or modifications may be made to the above-describedembodiments, without departing from the broad general scope of thepresent disclosure. The present embodiments are, therefore, to beconsidered in all respects as illustrative and not restrictive.

1. A propulsion device for progressing an instrument along a passage,the propulsion device comprising: an elongate tube comprising a firstend and a second end opposite the first end, the tube defining a channelconfigured to accommodate a liquid, a first end of the channel beingclosed at or near the first end of the tube and a second end of thechannel being defined by the second end of the tube; and a pressureactuator in communication with the second end of the channel andconfigured to selectively adjust a pressure of the liquid in the channelto alternatingly: reduce the pressure to induce cavitation and form gasbubbles in the liquid; and increase the pressure to collapse some or allof the gas bubbles back into the liquid, thereby accelerating at leastpart of the liquid towards the first end of the tube and transferringmomentum to the tube to progress the tube along the passage.
 2. Thepropulsion device of claim 1, further comprising one or more mechanismsconfigured to promote cavitation in one or more regions of the channelwhen the pressure is reduced, wherein the one or more regions extendalong at least part of a length of the channel.
 3. The propulsion deviceof claim 2, wherein the one or more mechanisms are configured to promotecavitation in a plurality of regions spaced along at least part of thelength of the channel.
 4. The propulsion device of claim 3, wherein theone or more mechanisms comprise a surface variation on an internalsurface of the channel.
 5. The propulsion device of claim 4, wherein thesurface variation comprises a coating.
 6. The propulsion device of claim5, wherein the coating comprises a hydrophobic material.
 7. Thepropulsion device of claim 5 or 6, wherein the coating comprises acatalytic material.
 8. The propulsion device of claim 5, wherein thecoating comprises one or more coatings selected from:octadecyltrichlorosilane, silane compounds, Parylene C, flouropolymers,PTFE (Teflon™), manganese oxide polystyrene (MnO2/PS), nano-compositezinc oxide polystyrene (ZnO/PS), nano-composite precipitated calciumcarbonate, fluorinated acrylate oligomers, urethane, acrylic,polyvinylpyrrolidone (PVP), polyethylene oxide, combinations ofhydroxyethylmethacrylate, and acrylamides.
 9. The propulsion device ofany one of claims 5 to 8, wherein the surface variation comprises atopographical variation.
 10. The propulsion device of claim 9, whereinthe topographical variation comprises a scratched or pitted surface. 11.The propulsion device of claim 9 or 10, wherein the topographicalvariation defines a plurality of V-shaped channels.
 12. The propulsiondevice of claim 11, wherein a characteristic angle of the V-shapedchannels is in the range of about 10° to 90°.
 13. The propulsion deviceof claim 11 or 12, wherein an average width of the V-shaped channels isin the range of about 1 μm to 10 μm.
 14. The propulsion device of anyone of claims 9 to 13, wherein the topographical variation defines aplurality of conical pits.
 15. The propulsion device of claim 14,wherein a characteristic angle of the conical pits is in the range ofabout 10° to 90°.
 16. The propulsion device of claim 14 or 15, whereinan average width of the conical pits is in the range of about 1 μm to 10μm.
 17. The propulsion device of any one of claims 9 to 16, wherein thetopographical variation defines a plurality of protrusions.
 18. Thepropulsion device of claim 17, wherein an average height of theprotrusions is in the range of about 0.1 μm to 1 mm.
 19. The propulsiondevice of claim 17 or 18, wherein an average width of the protrusions isin the range of about 0.1 μm to 500 μm.
 20. The propulsion device of anyone of claims 17 to 19, wherein an average distance between adjacentprotrusions is in the range of about 0.1 μm to 500 μm.
 21. Thepropulsion device of any one of claims 9 to 20, wherein thetopographical variation has a surface roughness in the range of about0.1 μm to 500 μm.
 23. The propulsion device of any one of claims 9 to21, wherein the topographical variation defines a porous surface. 24.The propulsion device of claim 23, wherein an average pore size of theporous surface is in the range of about 10 nm to 200 μm.
 25. Thepropulsion device of any one of claims 2 to 24, wherein the one or moremechanisms comprise a variation in a thermal conductivity of a wall ofthe tube along the length of the channel.
 26. The propulsion device ofclaim 25, wherein the thermal conductivity of the wall varies along thelength of the channel over a range of about 0.25 Wm⁻¹ K⁻¹ to 240Wm-1K-1.
 27. The propulsion device of any one of claims 2 to 26, whereinthe one or more mechanisms comprise one or more acoustic transducers.28. The propulsion device of claim 27, wherein one or more of theacoustic transducers are disposed within a wall of the tube.
 29. Thepropulsion device of claim 27 or 28, wherein one or more of the acoustictransducers are disposed outside of a wall of the tube.
 30. Thepropulsion device of any one of claims 27 to 29, wherein an operatingfrequency of the acoustic transducers is in the range of about 1 kHz to100 kHz.
 31. The propulsion device of any one of claims 27 to 30,wherein a power associated with insonation energy directed to a lumen ofthe channel by the acoustic transducers is in the range of about 10 mWto 100 mW.
 32. The propulsion device of any one of claims 1 to 31,wherein the device is configured for progressing a medical instrumentalong a lumen within a patient.
 33. The propulsion device of any one ofclaims 1 to 32, wherein the channel is a continuous enclosed channelextending from the first end of the tube to the second end of the tube.34. The propulsion device of any one of claims 1 to 33, wherein the tubeis reinforced against expansion or contraction due to internal pressurechanges.
 35. The propulsion device of any one of claims 1 to 34, whereinthe tube is formed of a material suitable for sterilisation.
 36. Thepropulsion device of any one of claims 1 to 35, further comprising aplurality of the tubes of any one of claims 1 to 31 extending side byside.
 37. The propulsion device of any one of claims 1 to 36, whereinthe pressure actuator comprises a flexible membrane defining a sealedchamber and a driving mechanism configured to deform the flexiblemembrane to selectively adjust the pressure of the liquid in thechannel.
 38. The propulsion device of any one of claims 1 to 36, whereinthe pressure actuator comprises: a piston assembly including a moveablepiston disposed within a bore of the piston assembly; and a drivingmechanism configured to drive the piston of the piston assembly toselectively adjust the pressure of the liquid in the channel.
 39. Thepropulsion device of claim 38, wherein the piston assembly is connectedto the tube to form a sealed tube unit containing the liquid, andwherein the piston assembly is removably coupleable to the drivingmechanism.
 40. A propulsion tube unit comprising: one or more of thetubes according to any one of claims 1 to 36; and a piston assemblyconnected to the second end of the tube, the piston assembly comprising:a body defining a bore in fluid communication with the channel of eachof the one or more tubes; and a movable piston disposed within the boreand configured to seal against an internal surface of the bore.
 41. Thepropulsion tube unit of claim 40, wherein the piston assembly and theone or more tubes cooperate to define a sealed vessel containing aselected mass of liquid and a selected mass of gas.
 42. A propulsiontube unit comprising: one of the tubes according to any one of claims 1to 36; and a movable piston disposed within the channel at or near thesecond end of the tube and configured to seal against an internalsurface of the channel.
 43. The propulsion tube unit of claim 42,wherein the piston and the tube cooperate to define a sealed vesselcontaining a selected mass of liquid and a selected mass of gas.
 44. Apropulsion tube unit comprising: an elongate tube comprising a first endand a second end opposite the first end, the tube defining a channelconfigured to accommodate a liquid, a first end of the channel beingclosed at or near the first end of the tube and a second end of thechannel being defined by the second end of the tube; and a pistonassembly connected to the second end of the tube, the piston assemblycomprising: a body defining a bore in fluid communication with thechannel of the tube; and a movable piston disposed within the bore andconfigured to seal against an internal surface of the bore, wherein thepiston assembly and the tube cooperate to define a sealed vesselcontaining a selected mass of liquid and a selected mass of gas.
 45. Apropulsion tube unit according to claim 44, wherein the piston assemblyis configured for cooperation with an actuator to effect movement of thepiston to selectively adjust a pressure of the liquid in the channel toalternatingly: reduce the pressure to induce cavitation and form gasbubbles in the liquid; and increase the pressure to collapse some or allof the gas bubbles back into the liquid, thereby accelerating at leastpart of the liquid towards the first end of the tube and transferringmomentum to the tube to progress the tube along the passage.
 46. Apropulsion tube unit according to claim 44 or 45, further comprising oneor more mechanisms configured to promote cavitation in a plurality ofregions spaced along at least part of the length of the channel when thepressure is reduced.
 47. A propulsion tube unit according to any one ofclaims 44 to 46, wherein the tube defines a plurality of channels, eachconfigured to accommodate a liquid, a first end of each channel beingclosed at or near the first end of the tube and a second end of eachchannel being defined by the second end of the tube, and wherein theplurality of channels are all in fluid communication with each other andwith the bore of the piston assembly.
 48. A drive console comprising: ahousing defining a socket configured to receive and engage a propulsiontube unit according to any one of claims 40 to 47; an actuatorconfigured to engage the piston; and a controller configured to operatethe actuator to move the piston to selectively adjust a pressure withinthe channel of the tube.
 49. A method of progressing an instrument alonga passage, the method comprising selectively adjusting a pressure of aliquid within a tube connected to the instrument to successively inducecavitation of gas bubbles in the liquid and subsequently collapse thegas bubbles back into the liquid to accelerate the liquid within thetube, transfer momentum from the liquid to the tube, and progress thetube along the passageway.
 50. The steps, processes, sub-processes,features, integers, structures, components, sub-components, systems,sub-systems, elements, compositions and/or compounds disclosed herein orindicated in the specification of this application individually orcollectively, and any and all combinations of two or more of said steps,processes, sub-processes, features, integers, structures, components,sub-components, systems, sub-systems, elements, compositions and/orcompounds.